1. Field of the Invention
The present invention relates generally to methods for manufacture of integrated circuit devices upon semiconductor substrates possessing oxide isolation regions. More particularly, the present invention relates to a method for using within the fabrication of integrated circuit devices upon a semiconductor substrate portions of masking structures used for forming oxide isolation regions upon the semiconductor substrate.
2. Description of Related Art
Integrated circuits are typically fabricated upon semiconductor substrates within and upon whose surfaces are formed resistors, transistors, diodes, capacitors and other electrical circuit elements. These electrical circuit elements are connected internally and externally to the semiconductor substrate upon which they are formed through conductor metallization layers which are separated by insulator layers.
In order to assure optimal performance of advanced integrated circuits it is important that individual integrated circuit devices within those integrated circuits be sufficiently electrically isolated from one another. The method through which this electrical isolation has traditionally most commonly been accomplished is through formation of Field OXide (FOX) isolation regions surrounding discrete integrated circuit devices or integrated circuit device cells. FOX isolation regions are commonly formed through a LOCal Oxidation of Silicon (LOCOS) method whereby portions of a silicon semiconductor substrate exposed through a LOCOS oxidation mask structure are oxidized to form FOX isolation regions. The more advanced LOCOS oxidation mask structures, such as Polysilicon Buffered LOCOS (PBLOCOS) employ multiple layers of masking materials to achieve fine line-width and defect-free FOX regions which substantially reduce parasitic effects between adjoining integrated circuit devices or device cells.
Masking layers which are typically employed in a PBLOCOS oxidation mask structure for forming FOX isolation regions upon a semiconductor substrate include: (1) a blanket pad oxide layer immediately adjoining a semiconductor substrate, (2) a blanket polysilicon buffer layer upon the blanket pad oxide layer, which blanket polysilicon buffer layer absorbs stresses due to variations in coefficients of thermal expansion of masking layers within the LOCOS oxidation mask structure, and (3) a patterned silicon nitride insulating layer which provides a surface impervious to the oxidation environment to which exposed portions of the blanket polysilicon buffer layer and the blanket pad oxide layer will subsequently be exposed when forming FOX isolation regions. Subsequent to forming FOX isolation regions, the masking layers are typically stripped from the surface of the semiconductor substrate to leave remaining active regions of a semiconductor substrate which are defined by the FOX isolation regions within and upon the semiconductor substrate. Within the active regions are then formed the electrical circuit elements to be interconnected to form integrated circuits upon the semiconductor substrate.
Although the PBLOCOS method has served well in providing functional and reliable FOX isolation regions within integrated circuits, the multiple masking processes employed within the PBLOCOS method may be involved and time consuming. The problem to which the present invention is directed is to effectively utilize within semiconductor structures to be formed upon active semiconductor substrate regions protected beneath PBLOCOS oxidation mask structures portions of those PBLOCOS oxidation mask structures which previously protected those active semiconductor substrate regions. By using portions of those PBLOCOS oxidation mask structures when forming integrated circuit device structures upon active semiconductor substrate regions previously protected by those PBLOCOS oxidation mask structures, there may be designed an economical integrated circuit manufacturing process which efficiently uses PBLOCOS oxidation mask structures.
Methods through which PBLOCOS oxidation mask structures may be formed and modified upon semiconductor substrates are known in the art. For example, Hodges et at. in U.S. Pat. Nos. 5,260,229 and 5,338,968 disclose methods by which exposed edges of polysilicon buffer layers within PBLOCOS oxidation mask structures may be masked such that those exposed polysilicon buffer layer edges are not susceptible to oxidation when the semiconductor substrate upon which is formed the PBLOCOS oxidation mask structure is exposed to an oxidizing environment. In addition, Tuan et al. in U.S. Pat. No. 5,338,750 disclose a method for forming and removing a LOCOS oxidation mask structure from a semiconductor substrate whereby pits are not formed in the semiconductor substrate upon which resided the LOCOS oxidation mask structure.
Desirable in the art are methods through which portions of a PBLOCOS oxidation mask structure employed in forming FOX isolation regions upon a semiconductor substrate may be employed in forming portions of integrated circuit device structures upon the semiconductor substrate region which the PBLOCOS oxidation mask structure protected. Such methods would provide for economical manufacturing processes which efficiently utilize the materials from which PBLOCOS oxidation mask structures are formed. Moreover, such methods may also provide for reductions in defect densities attributable to processes through which PBLOCOS oxidation mask structures are removed. Such reductions in defect densities would, in turn, provide higher semiconductor yields.